1. Field of the Invention
This invention relates generally to communication systems, and, more particularly, to wireless communication systems.
2. Description of the Related Art
A conventional wireless communication system provides wireless connectivity to numerous access terminals such as the cellular telephones, personal data assistants, smart phones, pagers, text messaging devices, global positioning devices, notebook computers, desktop computers, and the like. For example, access networks in the wireless communication system may provide wireless connectivity to access terminals located in geographical areas, or cells, associated with the access networks. To initiate a call session, an idle access terminal transmits a call request (or connection request) to one or more access networks to provide wireless connectivity to the cell that includes the access terminal. If the access network has sufficient capacity to support a new call, then the access network may transmit a message granting the access terminal's call request. The requested call session may be initiated and the access terminal may enter the active state. However, not all call requests are granted.
A call request from an access terminal may be denied because the system is overloaded and lacks sufficient capacity to support a new call. For example, the access network may not have sufficient radio frequency resources to support an air interface between the access network and the access terminal and may therefore deny the request. In other situations, there may not be sufficient backhaul capacity to support adding an additional call in the wireless communication system. In yet other situations, the processor occupancy associated with processors in the base station or access network may be too high to support an additional call. When the call request from an access terminal is denied, the access network transmits a message to the access terminal indicating that the call request has been denied. However, the access network does not provide any indication of the future accessibility of the wireless communication system.
Access terminals typically respond to a call request denial using an apersistence procedure in which the access terminal waits for a random period of time before starting the access procedure again. However, the likelihood that the new call request will be denied may remain high when the access channels, and/or other parts of the wireless communication system, are heavily loaded or overloaded at least in part because the re-access procedure is a random activity. Continuing to attempt to re-access a heavily loaded or overloaded access network may exacerbate the overloading by consuming radiofrequency and/or processor resources associated with the access channels.
Access terminals may use data over signaling (DoS) techniques to transmit data using signaling channels such as the access channel. For example, access terminals may use DoS to initiate a push-to-talk (PTT) call. The DoS techniques typically bypass the admission control algorithms used to allocate traffic channels and therefore may result in a call request being admitted when traffic channels or other radiofrequency resources are not available to support the call. Consequently, attempting to access a heavily loaded or overloaded access terminal using DoS techniques may lead to undesirable end results such as false grants, phantom calls, and the like. Since the access terminal is typically unaware of the current and/or future accessibility of the wireless communication system, the system may continue to attempt to access the wireless communication system using DoS techniques, which may exacerbate the aforementioned problems.